Object Oriented Design Principles Cheat Sheet

Thanks to the original writer and article :

https://senoritadeveloper.medium.com/

TL;DR

My aim here is not to go into detail but create a cheat sheet to quickly review before interviews to serve as a reminder.

OOP Concepts

• Abstraction?(hide complexity — blackbox, show only essential details. interfaces, abstract classes)
• Encapsulation?(private fields, public getter/setter. code update in one place)
• Inheritance
• Polymorphism?(method overloading, method overriding)

Cohesion & Coupling

Cohesion?= how related the functions within a single module are

Coupling?= interdependencies between modules

High Cohesion, Low Coupling ????

SOLID Principles

• Single Responsibility
• Open-Closed Principle?(open for extension, closed for modification)
• Liskov’s Substitution?(Rabbit extends Animal. classes should be substitutable)
• Interface Segregation?(instead of a single interface, prefer multiple smaller interfaces)
• Dependency Inversion?(Decoupling. depend on abstractions, and interfaces)

GOF?=> interface > implementation, object decomposition > inheritance

Design Patterns

(Creational — Structural — Behavioral)

Creational

• Factory Method
• Abstract Factory?(factory of factories)
• Builder?(complex objects using smaller objects)
• Prototype?(cloning)
• Singleton?(single instance)

Structural

• Adapter?(incompatible interfaces)
• Bridge?(decouple an abstraction from its implementation)
• Composite?(a class that contains group of its own objects)
• Decorator?(wrapper / no modifications on existing class, new functionality added)
• Facade?(hides complexity)
• Flyweight?(reduce weight of object creation, create if needed or reuse)
• Proxy?(a class represents functionality of another class — create a proxy class having original object)

Behavioral

• Chain of Responsibility
• Command?(stock.buy returns BuyStock, stock.sell returns SellStock — both using Stock class)
• Interpreter?(language grammer, sql parsing)
• Iterator?(.next)
• Mediator?(communication between different classes)
• Memento?(restores to a previous state)
• Observer?(register, notify)
• State?(status, context)
• Null Object?(for do-nothing relationship, instead of returning null value)
• Strategy?(a class behavior or its algorithm can change at runtime)
• Template?(abstract class, method flow)
• Visitor?(execution algorithm of element can vary as and when visitor varies)
• MVC

Happy Coding!